Long term seagrass monitoring in the Port of Thursday Island: March 2008

Seagrass habitats are valuable fisheries resources that show measurable responses to changes in water quality. These attributes make seagrass meadows ideal candidates for monitoring the long term health of marine environments. A network of long term seagrass monitoring sites has been established at various port locations throughout Queensland to assist port managers in the planning and development of port operations to achieve minimal impacts on the marine environment and fish habitats. The programs are also used as an indicator of the overall marine environmental health of ports and are an example of international best practise in the management of port environments. This report details the latest findings from the Port of Thursday Island long term seagrass monitoring program from the most recent survey conducted in March 2008.\ud \ud A baseline survey of seagrass habitat at the Port of Thursday Island in March 2002 identified some of the best examples of intertidal and subtidal seagrass habitat that have been found in Queensland. Nine seagrass meadows were selected for long term monitoring from the original baseline survey. The monitoring meadows were representative of the range of seagrass communities identified and encompassed those meadows located in areas likely to be vulnerable to impacts from port operations and developments. This current survey is the third of planned biennial long-term seagrass monitoring, with previous surveys conducted in March 2004 and 2006. The monitoring program assesses seagrass above ground biomass, individual meadow area and species composition (community types) and compares changes with previous surveys.\ud \ud The results of the March 2008 monitoring survey found that seagrasses in the Port of Thursday Island were generally in good condition. Seagrass meadow area was similar to that detected during previous monitoring while coastal meadows dominated by Halodule and Halophila were at similar densities to previous surveys. However, meadows dominated by the large growing species Enhalus acoroides appear to have been under greater stress in recent years resulting in a decline in density. These declines in Enhalus meadows are thought to be in response to a combination of natural climate and exposure related drivers but their continuing decline may be cause for concern in the future. As monitoring is only conducted every two years, the exact cause of these declines is difficult to interpret. However these changes were consistent with changes that had occurred for the same species in other nearby monitoring locations and were unlikely to be due to human or port activities